The Fix
pip install pydantic==2.9.1
Based on closed pydantic/pydantic issue #10328 · PR/commit linked
Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.
@@ -139,7 +139,7 @@ jobs:
run: |
pdm venv create --with-pip --force $PYTHON
- pdm install -G testing -G email
+ pdm install -G testing -G email -G timezone
Option A — Upgrade to fixed release\npip install pydantic==2.9.1\nWhen NOT to use: This fix is not suitable for users who require `tzdata` on all platforms.\n\n
Why This Fix Works in Production
- Trigger: Users on non-Windows systems faced unnecessary installation requirements for timezone data.
- Mechanism: The `tzdata` dependency was unnecessarily required for all installations of Pydantic
- Why the fix works: Turns the `tzdata` dependency into an optional dependency group `timezone`, making it conditional for users who need it. (first fixed release: 2.9.1).
- If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.
Why This Breaks in Prod
- The `tzdata` dependency was unnecessarily required for all installations of Pydantic
- Production symptom (often without a traceback): Users on non-Windows systems faced unnecessary installation requirements for timezone data.
Proof / Evidence
- GitHub issue: #10328
- Fix PR: https://github.com/pydantic/pydantic/pull/10331
- First fixed release: 2.9.1
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.79
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“@jakob-keller, Thanks for the report. Not sure if that qualifies as a bug, but we can certainly consider making this optional! Would very much appreciate…”
“OK, I'll give it a shot! Should I follow the polars example then?”
“Yep, that works. You can treat it like we do for the [email] add-on for email validator.”
Failure Signature (Search String)
- Users on non-Windows systems faced unnecessary installation requirements for timezone data.
Copy-friendly signature
Failure Signature
-----------------
Users on non-Windows systems faced unnecessary installation requirements for timezone data.
Error Message
Signature-only (no traceback captured)
Error Message
-------------
Users on non-Windows systems faced unnecessary installation requirements for timezone data.
Environment
- Pydantic: 2
What Broke
Users on non-Windows systems faced unnecessary installation requirements for timezone data.
Why It Broke
The `tzdata` dependency was unnecessarily required for all installations of Pydantic
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install pydantic==2.9.1
Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.
Fix reference: https://github.com/pydantic/pydantic/pull/10331
First fixed release: 2.9.1
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- This fix is not suitable for users who require `tzdata` on all platforms.
Did This Fix Work in Your Case?
Quick signal helps us prioritize which fixes to verify and improve.
Prevention
- Add a CI check that diffs key outputs after upgrades (OpenAPI schema snapshots, JSON payload shapes, CLI output).
- Upgrade behind a canary and run integration tests against the canary before 100% rollout.
Version Compatibility Table
| Version | Status |
|---|---|
| 2.9.1 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.